Environmental Engineering Reference
In-Depth Information
forage (woody twigs).The rate of heat loss to the environment is propor-
tional to the difference in surface temperature of a body and the tempera-
ture of the surrounding environment.To lower the rate of heat loss, deer
increase the thickness of their undercoat to decrease the amount of warm,
bare skin exposed to the cold elements. In addition, the thin legs of deer
have a high surface area to body volume ratio.This is akin to having large
picture windows in a tiny bungalow. Essentially, considerable amounts of
heat within the core of the house (or the deer's leg) will radiate out to the
environment because there are many large yet poorly insulated surfaces over
which heat is quickly exchanged with the environment.To reduce heat loss
deer restrict the amount of warm blood flowing to these extremities and
they lay down fat to insulate the extremities with body tissue that is not
highly prone to freezing. Deer also compensate for poor quality forage by
lowering their metabolic rate during winter to decrease their demand for
food energy.These changes are reversed with the onset of warmer temper-
atures and better quality forage in spring.
Climatic Conditions and Performance
Different species are located in different geographic regions in part because
they have different capacities to deal with regional differences in climatic
conditions. For example, consider two species that have different abilities to
tolerate temperature and direct solar radiation. Differences in temperature
tolerance may arise because some species such as birds and mammals have
feathers or fur that insulate their body whereas other species such as reptiles
and amphibians do not. Differences in solar radiation tolerance may arise
because of differences in the color of the body surface, which determines
the amount of solar radiation absorbed: darker surfaces absorb more solar
energy than do lighter surfaces.We can depict these species-specific abili-
ties to tolerate temperature and solar radiation by plotting individual fitness
(that is individual survival and reproduction) against temperature and against
absorbed solar radiation (figure 3.3).These curves can be determined ex-
perimentally by placing individuals of a species in different temperature
regimes, while holding the amount of incoming solar radiation constant,
and by placing individuals in different solar radiation regimes while hold-
ing temperature constant.The net result is that we tend to find that indi-
viduals of a species have a temperature or solar radiation level where they
exhibit peak performance (high fitness) and there are neighboring temper-
atures or radiation regimes where they can perhaps do all right (medium to
